The background of this invention pertaining to the detection of discontinuities in a flowing fluid stream is set out in my U.S. Pat. Nos. 4,112,773 and 4,214,484, both hereby incorporated by reference. The ultrasonic detection devices disclosed in those patents can detect particles in a flow as small as 10 microns in diameter with the same degree of accuracy that the prior art only obtained with particles ten times larger. In both these inventions, a portion of the conduit through which the fluid flows is used as a lens (i.e., the natural curvature of the inside of the conduit acts as the inside face of the lens) to focus the ultrasonic beam. The conduit, however, which may be an already existing pipe section or a specially fabricated one, apparently contain many small flaws throughout, and the flaws will scatter a portion of an ultrasonic beam passing therethrough thereby reducing the overall beam energy. Similarly, metal conduit will have grains, which also will scatter the beam to some degree. This loss of energy is important because the reflected signals from the tiny discontinuities are very small in magnitude to begin with, and scattering and other losses reduce the amount of energy available to be reflected. By the same token, even minor noise levels present a serious problem. However, in the past, the prior art fluid discontinuity detection devices have for the most part disregarded noise problems, and the only ultrasonic detectors even partially protected from noise have been the non-destructive workpiece testing devices, which usually operate in extremely noisy environments, e.g., in close proximity to metal working equipment.
In addition to detecting discontinuities in a standing fluid or in a flow, it is often desirable to be able to determine the composition of the fluid itself. For example, in certain chemical processes, two or more liquid components may be mixed together to form a homogeneous fluid, and the percentages of the components may vary. While the change in the amount of some of the components within certain limits may be acceptable, a minor change in the percentage of a certain component may ruin the entire process. Accordingly, it is important to be able to detect any change in percentages of the components and to identify the component or components which change. This cannot be done with the prior art detection devices, which are limited to dealing either with immiscible liquids (e.g., determining the location of the interface between them) or with solids or slurries in the flow (e.g., measuring the scattering caused by these solids or semi-solids to determine the percentage of solids or semi-solids in the flow).